11 research outputs found

    Xenotransplantation Policies: Italy and The Holy See

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    from the Table of Contents: Introduction; Italy; The Holy See; Annexes

    Structural evolution after oxidative pretreatment and CO oxidation of Au nanoclusters with different ligand shell composition: a view on the Au core

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    The reactivity of supported monolayer protected Au nanoclusters is directly affected by their structural dynamics under pretreatment and reaction conditions. The effect of different types of ligands of Au clusters supported on CeO2_2 on their core structure evolution, under oxidative pretreatment and CO oxidation reaction, was investigated. X-ray absorption and X-ray photoelectron spectroscopy studies revealed that the clusters evolve to a similar core structure above 250 °C in all the cases, indicating the active role of the ligand–support interaction in the reaction

    Directing Intrinsic Chirality in Gold Nanoclusters: Preferential Formation of Stable Enantiopure Clusters in High Yield and Experimentally Unveiling the “Super” Chirality of Au144_{144}

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    Chiral gold nanoclusters offer significant potential for exploring chirality at a fundamental level and for exploiting their applications in sensing and catalysis. However, their widespread use is impeded by low yields in synthesis, tedious separation procedures of their enantiomeric forms, and limited thermal stability. In this study, we investigated the direct synthesis of enantiopure chiral nanoclusters using the chiral ligand 2-MeBuSH in the fabrication of Au25_{25}, Au38_{38}, and Au144_{144} nanoclusters. Notably, this approach leads to the unexpected formation of intrinsically chiral clusters with high yields for chiral Au38_{38} and Au144_{144} nanoclusters. Experimental evaluation of chiral activity by circular dichroism (CD) spectroscopy corroborates previous theoretical calculations, highlighting the stronger CD signal exhibited by Au144_{144} compared to Au38_{38} or Au25_{25}. Furthermore, the formation of a single enantiomeric form is experimentally confirmed by comparing it with intrinsically chiral Au38_{38}(2-PET)24_{24} (2-PET: 2-phenylethanethiol) and is supported theoretically for both Au38_{38} and Au144_{144}. Moreover, the prepared chiral clusters show stability against diastereoisomerization, up to temperatures of 80°C. Thus, our findings not only demonstrate the selective preparation of enantiopure, intrinsically chiral, and highly stable thiolate-protected Au nanoclusters through careful ligand design but also support the predicted “super” chirality in the Au144_{144} cluster, encompassing hierarchical chirality in ligands, staple configuration, and core structure

    Ligand exchange reactions of Au nanoclusters

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    Die Eigenschaften von ligandenstabilisierten Au Nanoclustern werden sowohl durch deren GrĂ¶ĂŸe, als auch durch die chemische Natur der Liganden beeinflusst. Modifikation derselben lĂ€sst sich mithilfe von Ligandenaustauschreaktionen bewerkstelligen, welche damit ausge-zeichnete Möglichkeiten zur gezielten VerĂ€nderung der Clustereigenschaften darstellen. Zudem können diese Reaktionen auch als Alternativstrategie zur Synthese von Clustern herangezogen werden, welche nicht aus den ĂŒblicherweise verwendeten Ausgangsstoffen zugĂ€nglich sind. FĂŒr praktische Anwendungen, z.B. als Katalysator oder als Sensor, werden die Cluster fĂŒr gewöhnlich auf oxidischen Supportmaterialien immobilisiert. Um ein besseres VerstĂ€ndnis derartiger Anwendungsprozesse und auch von Au Nanoclustern im Allgemeinen zu erlangen, sind Studien der Wechselwirkungen zwischen Cluster und Supportmaterial notwendig. Eine Möglichkeit dafĂŒr stellen Vergleiche der Ligandenaustauschreaktionen von gelösten und immobilisierten Clustern dar. Bislang wurden jedoch nur Untersuchungen der Ligandenaustauschreaktionen in flĂŒssiger Phase publiziert. Im Rahmen dieser Arbeit wurde zum ersten Mal ein Ligandenaustausch von immobilisierten Au11(PPh3)7Cl3 Nanoclustern mit Thiolliganden beobachtet. Zur Untersuchung der Austauschreaktionen wurden drei verschiedene Systeme verwendet: (1) freie Cluster in Lösung, (2) Cluster immobilisiert auf planaren Al2O3 oder ZnSe OberflĂ€chen und (3) Cluster abgelagert auf SiO2 oder Al2O3 Pulvern. FĂŒr die Reaktionen in Lösung konnte ein Wachstum der Cluster von Au11 zu Au25 beobachtet werden, jedoch nicht fĂŒr Cluster, die auf planaren OberflĂ€chen oder Pulvern immobilisiert waren. Im Fall der Systeme (1) und (2) war der Ligandenaustausch zudem nicht vollstĂ€ndig und fĂŒhrte zu Produkten, die sowohl Triphenylphosphin und Chlor, als auch Thiole als Liganden aufwiesen. FĂŒr jene Cluster, die auf Metalloxidpulvern immobilisiert wurden, ist die Anzahl der ausgetauschten Liganden noch Gegenstand laufender Untersuchungen. Zudem wurden auch Ligandenaustauschreaktionen von Au15 Nanoclustern in Lösung mit einem großen Überschuss an 2-Phenylethanthiol untersucht, wobei Au20(SC2H4Ph)16 entstand. Diese Reaktion stellt eine bisher unbekannte, unkompliziert durchzufĂŒhrende Synthese von Au20 Clustern in hoher Ausbeute dar.The properties of monolayer protected Au nanoclusters are known to be size-dependent, and strongly related to the nature of the protecting ligand. Modification of the surface ligands can be accomplished by a ligand exchange reaction. This represents a valuable pathway for tuning the cluster properties, as well as alternative synthetic pathways of cluster species, which cannot be easily obtained from standard precursor materials. For applications such as catalysis or sensing, the clusters are usually immobilized on metal oxides. For a better understanding of these processes and of Au nanoclusters in general, studying the interaction between cluster and support is crucial. One approach is provided by comparison of ligand exchange reactions of dissolved and deposited clusters. However, so far only ligand exchange reactions with Au nanoclusters in solution have been published. Within this thesis, ligand exchange of immobilized Au11(PPh3)7Cl3 clusters and thiol ligands is reported for the first time. The reactions were studied using three different systems: (1) free clusters in solution, (2) cluster dropcast films on planar Al2O3 or ZnSe and (3) clusters supported on SiO2 or Al2O3 powders. For the reaction in solution, growth of the cluster core from Au11 to Au25 was observed, whereas no major change in size was found for reactions with cluster dropcast films or clusters supported on oxide powder material. Only incomplete exchange was observed for system (1) and (2), with all triphenylphosphine, thiol and chloride being present in the ligand shell of the product. For the powder-supported clusters, the number of exchanged ligands remains to be identified in future work. In addition, ligand exchange in solution, starting from crude Au15 with a large excess of 2-phenylethanethiol was investigated, resulting in the formation of Au20(SC2H4Ph)16. This presents a new, facile approach for synthesizing Au20 clusters in high yield.11

    Der Ligand bestimmt den Cluster: Einfluss und Möglichkeiten zur Modifizierung der Liganden an Goldnanoclustern

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    Arbeit an der Bibliothek noch nicht eingelangt - Daten nicht geprĂŒftAbweichender Titel nach Übersetzung der Verfasserin/des VerfassersMonolayer-protected gold nanoclusters show interesting catalytic activity, as well as electronic,geometric and chiral properties that are very different from inert bulk gold and therefore of interest for a number of applications. Furthermore, such clusters can be obtained as monodisperse samples, which allows to investigate structure–property relationships. One of the most important factors that influence for example the size and shape, but also the stability, reactivity or chirality in Au nanoclusters are the protecting ligands, for which already a subtle change in the hydrocarbon framework can result in significantly different properties of the cluster species. Understanding and selectively tuning the metal nanoclusters by ligand engineering has thus become an important objective in nanocluster chemistry. Within this thesis, three fields in which protecting ligands play a major role are investigated,namely (1) chirality, (2) synthesis strategies for Au nanoclusters and (3) heterogeneous catalysis.Several species of gold nanoclusters exhibit intrinsic chiral properties, which can be due to chiral Au–ligand interfaces or chiral metal kernels. However, obtaining them as single enantiomers can be a daunting task since it requires specifically tailored separation techniques.Therefore, a direct synthesis approach with a chiral thiol ligand was employed to obtain two intrinsically chiral nanoclusters, Au38 and Au144, for which unusually high yields were achieved, whereas only moderate yields of an achiral Au25 cluster were obtained. Comparison of the circular dichroism spectra to reported single enantiomer Au38 and Au144 spectra indicated that enantiopure samples had been obtained. These results demonstrate that synthesis with chiral ligands is a powerful tool to selectively afford chiral gold nanoclusters in high yield.Furthermore, complementary density functional theory calculations of Au25 and Au38 were carried out to obtain suitable model structures for future investigation of their chiral properties.Another approach for targeted cluster design are ligand exchange induced size/structure transformations, in which a precursor gold cluster is subjected to large amounts of thiolate ligands and thereby selectively converted to a new cluster species of different size and/orgeometry. Applying such a two-phase LEIST process on the water-soluble Au25(SG)13 resulted in phase-transfer and formation of Au16(2-PET)14. Infrared spectroscopy confirmed complete replacement of the protecting ligands, whereas X-ray absorption spectroscopy indicated similar core structures of both clusters. Of note, Au16(2-PET)14 is among the smallest thiolate-protected Au nanoclusters that have been isolated in significant purity, which makes it an interesting compound for studying structural evolution of gold nanoclusters.Finally, also ligand effects in catalysis were investigated by studying CO oxidation as model reaction with Au nanoclusters protected by different types of ligands (phosphines, thiolates,mix of phosphines and thiolates). The lower conversion achieved by clusters with phosphines in the ligand shell compared to the thiolate-protected cluster after oxidative pretreatment at 250 °C was attributed to the accumulation of ligand residues at the cluster–support interface region. These sites are of great importance for the subsequent reaction. In contrast,no significant dependence on the availability of exposed Au surface or the cluster size was observed. This shows that the ligands influence the reactivity of cluster catalysts even after their decomposition, which must therefore be taken into account in the design of a catalytic system.Durch Liganden geschĂŒtzte Goldnanocluster zeigen bemerkenswerte katalytische AktivitĂ€t,sowie elektronische, geometrische und chirale Eigenschaften, die sich stark von jenen des unreaktiven Goldes in metallischer Form unterscheiden und dadurch fĂŒr eine Vielzahl von Anwendungen attraktiv sind. Zudem können solche Cluster auch monodispers hergestellt werden, was es ermöglicht, Struktur–Wirkungsbeziehungen zu untersuchen. Einer der bedeutendsten Einflussfaktoren auf beispielsweise die GrĂ¶ĂŸe und Form, aber auch die StabilitĂ€t und ReaktivitĂ€t oder ChiralitĂ€t von Goldnanoclustern entsteht durch die Liganden. Bereits eine kleine VerĂ€nderung im organischen Rest kann die Clustereigenschaften nachhaltig verĂ€ndern. Ein wichtiges Ziel der Goldnanoclusterchemie ist es daher, diese von den Liganden hervorgerufenen Änderungen zu verstehen und gezielt einsetzen zu können. Im Rahmen dieser Arbeit werden drei Bereiche, in denen Clusterliganden eine wichtige Rolle spielen,nĂ€her untersucht, und zwar (1) ChiralitĂ€t, (2) Synthesestrategien fĂŒr Goldnanocluster und(3) heterogene Katalyse. Einige Goldnanocluster zeigen intrinsisch chirale Eigenschaften, die durch chirale Au–Liganden Schnittstellen und/oder durch chirale Kernstrukturen hervorgerufen werden. Es ist jedoch oftmals ein kompliziertes Unterfangen, die Cluster als reine Enantiomere zu erhalten,da es den Einsatz speziell angepasster Separationstechniken erfordert. Daher wurde eine direkte Synthesestrategie mit einem chiralen Thiolliganden eingesetzt und zwei verschiedene intrinsisch chirale Nanocluster, nĂ€mlich Au38 und Au144, in ungewöhnlich hoher Ausbeute erhalten, wohingegen kein Anstieg in der Menge des erhaltenen achiralen Au25 Clusters beobachtet werden konnte. Ein Vergleich der gemessenen Circular Dichroism Spektren mit publizierten Spektren einzelner Enantiomere von Au38 und Au144 deutete darauf hin,dass enantiomerenreine Clusterproben erhalten wurden. Das zeigt, dass Direktsynthese mit chiralen Liganden ein sehr wirksames Mittel ist, um gezielt chirale Goldnanocluster in hoher Ausbeute zu erhalten.Zudem wurden auch Dichtefunktionalrechnungen der Au25 und Au38 Cluster durchgefĂŒhrt,mit dem Ziel, geeignete Modellstrukturen fĂŒr die weitere Untersuchung ihrer chiralen Eigenschaften zu erhalten. Zielgerichtetes Clusterdesign lĂ€sst sich aber beispielsweise auch durch sogenannte Ligandenaustausch-induzierte GrĂ¶ĂŸe/Struktur Transformationen bewerkstelligen. Dabei wird ein Ausgangscluster einer großen Menge an Thiolatliganden ausgesetzt und dadurch selektiv in einen anderen Cluster von unterschiedlicher GrĂ¶ĂŸe und/oder Geometrie ĂŒberfĂŒhrt.FĂŒhrt man einen solchen Austauschprozess als Zweiphasenreaktion (Wasser und organisches Lösungsmittel) mit dem wasserlöslichen Au25(SG)13 als Edukt durch, erfolgt ein Phasentransfer und die Bildung von Au16(2-PET)14. Infrarotspektroskopie zeigte, dass die Ligandenkomplett ausgetauscht wurden, wohingegen Röntgenabsorptionsspektroskopie auf Ă€hnliche Kerngeometrien der beiden Cluster hinwies. Bei Au16(2-PET)14 handelt es sich um einen der kleinsten Thiolat-geschĂŒtzen Goldnanocluster, die bisher in entsprechender Reinheit isoliert werden konnten. Das macht es zu einer interessanten Verbindung, um die strukturelle Evolution dieser Cluster zu untersuchen. Zuletzt wurden auch Ligandeneffekte in der Katalyse untersucht. HierfĂŒr wurde eine COOxidations-Modellreaktion mit Goldnanoclustern, die mit unterschiedlichen Arten von Liganden (Phosphine, Thiolate bzw. eine Mischung der beiden) in ihrer Struktur aufweisen,untersucht. Die geringere Umsetzung von CO mit den Clustern, die Phosphine in ihrer Ligandenaschale aufweisen, im Vergleich zum Thiolat-geschĂŒtzten Clusterkatalysator nach oxidativer Vorbehandlung bei 250 °C wurde auf die Ansammlung von LigandenĂŒberresten im Bereich der Schnittstelle zwischen Cluster und TrĂ€germaterial zurĂŒckgefĂŒhrt. Diese Positionen sindbei der CO Oxidation von großer Bedeutung. Im Gegensatz dazu konnte keine AbhĂ€ngigkeitvon der VerfĂŒgbarkeit freier GoldoberflĂ€che oder der ClustergrĂ¶ĂŸe nachgewiesen werden. Das zeigt, dass die Liganden die ReaktivitĂ€t von Clusterkatalysatoren beeinflussen, auch wenn sie bereits durch Vorbehandlung zersetzt wurden und muss daher beim Design des Katalysatorsystems berĂŒcksichtigt werden.20

    Ligand Migration from Cluster to Support : A Crucial Factor for Catalysis by Thiolate-protected Gold Clusters

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    Thiolate protected metal clusters are valuable precursors for the design of tailored nanosized catalysts. Their performance can be tuned precisely at atomic level, e. g. by the configuration/type of ligands or by partial/complete removal of the ligand shell through controlled pre-treatment steps. However, the interaction between the ligand shell and the oxide support, as well as ligand removal by oxidative pre-treatment, are still poorly understood. Typically, it was assumed that the thiolate ligands are simply converted into SO, CO and HO. Herein, we report the first detailed observation of sulfur ligand migration from Au to the oxide support upon deposition and oxidative pre-treatment, employing mainly S K-edge XANES. Consequently, thiolate ligand migration not only produces clean Au cluster surfaces but also the surrounding oxide support is modified by sulfur-containing species, with pronounced effects on catalytic properties

    Ligand engineering of immobilized nanoclusters on surfaces: ligand exchange reactions with supported Au<sub>11</sub>(PPh<sub>3</sub>)<sub>7</sub>Br<sub>3</sub>

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    The properties of gold nanoclusters, apart from being size-dependent, are strongly related to the nature of the protecting ligand. Ligand exchange on Au nanoclusters has been proven to be a powerful tool for tuning their properties, but has so far been limited to dissolved clusters in solution. By supporting the clusters previously functionalized in solution, it is uncertain that the functionality is still accessible once the cluster is on the surface. This may be overcome by introducing the desired functionality by ligand exchange after the cluster deposition on the support material. We herein report the first successful ligand exchange on supported (immobilized) Au11 nanoclusters. Dropcast films of Au11(PPh3)7Br3 on planar oxide surfaces were shown to react with thiol ligands, resulting in clusters with a mixed ligand shell, with both phosphines and thiolates being present. Laser ablation inductively coupled plasma mass spectrometry and infrared spectroscopy confirmed that the exchange just takes place on the cluster dropcast. Contrary to systems in solution, the size of the clusters did not increase during ligand exchange. Different structures/compounds were formed depending on the nature of the incoming ligand. The feasibility to extend ligand engineering to supported nanoclusters is proven and it may allow controlled nanocluster functionalization

    Synthesis and Properties of Monolayer Protected Cox(SC2H4Ph)m Nanoclusters

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    This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see .Nanometer-sized and stable thiolate-protected cobalt clusters were synthesized by a wet chemical method, leading to a pink solution with well-defined optical activity (UV-Vis) and photoluminescence (PL). The cobalt cluster core of ~1.3 nm size was metallic (as indicated by STEM, STM, XPS, HAADF-EELS) and was surrounded by a specific configuration of thiolate staples (according to Raman, FTIR, XAFS, MALDI) that is similar to that of corresponding gold clusters.Austrian Science Funds (FWF)1094810956

    Directing Intrinsic Chirality in Gold Nanoclusters : Preferential Formation of Stable Enantiopure Clusters in High Yield and Experimentally Unveiling the “Super” Chirality of Au144

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    Chiral gold nanoclusters offer significant potential for exploring chirality at a fundamental level and for exploiting their applications in sensing and catalysis. However, their widespread use is impeded by low yields in synthesis, tedious separation procedures of their enantiomeric forms, and limited thermal stability. In this study, we investigated the direct synthesis of enantiopure chiral nanoclusters using the chiral ligand 2-MeBuSH in the fabrication of Au25, Au38, and Au144 nanoclusters. Notably, this approach leads to the unexpected formation of intrinsically chiral clusters with high yields for chiral Au38 and Au144 nanoclusters. Experimental evaluation of chiral activity by circular dichroism (CD) spectroscopy corroborates previous theoretical calculations, highlighting the stronger CD signal exhibited by Au144 compared to Au38 or Au25. Furthermore, the formation of a single enantiomeric form is experimentally confirmed by comparing it with intrinsically chiral Au38(2-PET)24 (2-PET: 2-phenylethanethiol) and is supported theoretically for both Au38 and Au144. Moreover, the prepared chiral clusters show stability against diastereoisomerization, up to temperatures of 80 °C. Thus, our findings not only demonstrate the selective preparation of enantiopure, intrinsically chiral, and highly stable thiolate-protected Au nanoclusters through careful ligand design but also support the predicted “super” chirality in the Au144 cluster, encompassing hierarchical chirality in ligands, staple configuration, and core structure.peerReviewe

    Perinatal care at the limit of viability between 22 and 26 completed weeks of gestation in Switzerland : 2011 revision of the Swiss recommendations

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    Perinatal care of pregnant women at high risk for preterm delivery and of preterm infants born at the limit of viability (22-26 completed weeks of gestation) requires a multidisciplinary approach by an experienced perinatal team. Limited precision in the determination of both gestational age and foetal weight, as well as biological variability may significantly affect the course of action chosen in individual cases. The decisions that must be taken with the pregnant women and on behalf of the preterm infant in this context are complex and have far-reaching consequences. When counselling pregnant women and their partners, neonatologists and obstetricians should provide them with comprehensive information in a sensitive and supportive way to build a basis of trust. The decisions are developed in a continuing dialogue between all parties involved (physicians, midwives, nursing staff and parents) with the principal aim to find solutions that are in the infant's and pregnant woman's best interest. Knowledge of current gestational age-specific mortality and morbidity rates and how they are modified by prenatally known prognostic factors (estimated foetal weight, sex, exposure or nonexposure to antenatal corticosteroids, single or multiple births) as well as the application of accepted ethical principles form the basis for responsible decision-making. Communication between all parties involved plays a central role. The members of the interdisciplinary working group suggest that the care of preterm infants with a gestational age between 22 0/7 and 23 6/7 weeks should generally be limited to palliative care. Obstetric interventions for foetal indications such as Caesarean section delivery are usually not indicated. In selected cases, for example, after 23 weeks of pregnancy have been completed and several of the above mentioned prenatally known prognostic factors are favourable or well informed parents insist on the initiation of life-sustaining therapies, active obstetric interventions for foetal indications and provisional intensive care of the neonate may be reasonable. In preterm infants with a gestational age between 24 0/7 and 24 6/7 weeks, it can be difficult to determine whether the burden of obstetric interventions and neonatal intensive care is justified given the limited chances of success of such a therapy. In such cases, the individual constellation of prenatally known factors which impact on prognosis can be helpful in the decision making process with the parents. In preterm infants with a gestational age between 25 0/7 and 25 6/7 weeks, foetal surveillance, obstetric interventions for foetal indications and neonatal intensive care measures are generally indicated. However, if several prenatally known prognostic factors are unfavourable and the parents agree, primary non-intervention and neonatal palliative care can be considered. All pregnant women with threatening preterm delivery or premature rupture of membranes at the limit of viability must be transferred to a perinatal centre with a level III neonatal intensive care unit no later than 23 0/7 weeks of gestation, unless emergency delivery is indicated. An experienced neonatology team should be involved in all deliveries that take place after 23 0/7 weeks of gestation to help to decide together with the parents if the initiation of intensive care measures appears to be appropriate or if preference should be given to palliative care (i.e., primary non-intervention). In doubtful situations, it can be reasonable to initiate intensive care and to admit the preterm infant to a neonatal intensive care unit (i.e., provisional intensive care). The infant's clinical evolution and additional discussions with the parents will help to clarify whether the life-sustaining therapies should be continued or withdrawn. Life support is continued as long as there is reasonable hope for survival and the infant's burden of intensive care is acceptable. If, on the other hand, the health care team and the parents have to recognise that in the light of a very poor prognosis the burden of the currently used therapies has become disproportionate, intensive care measures are no longer justified and other aspects of care (e.g., relief of pain and suffering) are the new priorities (i.e., redirection of care). If a decision is made to withhold or withdraw life-sustaining therapies, the health care team should focus on comfort care for the dying infant and support for the parents
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